It has been known for a number of years that homopolypropylene can be modified by grafting an unsaturated dibasic acid or acid anhydride moiety onto the polymer backbone. The polarity imparted to the otherwise nonpolar, highly inert polymer enables the polymer to be adhered to other polar substrates to which it would not ordinarily adhere.
Maleic modified polypropylene has been a commercial success in both the amorphous form and the crystalline form. Modification is effected up to about the 5% by weight level to provide good adhesion to, e.g., metals, glass, wood and polar polymers. In specific applications, the maleic modified polymer is employed as a coating for glass fibers which are to be used to reinforce shaped polyolefin objects, resulting in very significant increases in tensile strength and heat deflection temperature. In another application, the modified polymer is employed as a primer layer or is blended into the polypropylene to adhere polypropylene coatings to metal or to other polymers.
It has also been suggested in U.S. Pat. No. 3,433,777 to effect maleic anhydride modification of amorphous copolymers of propylene and 1-olefin including butene-1, hexene-1 and pentene-1. It is alleged that these modified polymers are useful in adhesives.